Studies on the simultaneous solid-state polymerization and exchange reactions of PET/PEN oligomer blends

Abstract

Poly(ethylene terephthalate) (PET) and poly(ethylene-2,6-naphthalate) PEN oligomers were obtained by degrading high molecular weight PET and PEN. Crystalline PET/PEN blends of varying compositions were prepared by melt blending and then crystallizing at 175°C. Simultaneous solid-state polymerization (SSP) and exchange reactions were performed on these blends by heating just below the melting temperature under a nitrogen flow. ¹H NMR spectroscopy was used to study the progress of exchange reactions between terephthalic and naphthalate units. The inherent viscosity was measured to monitor the progress of SSP. WAXS studies indicated that the condensation and exchange reactions occurred in the amorphous phase, leaving the PET and PEN crystallites unaffected. Detailed thermal characterization showed that the crystallization behavior of the copolymers depended strongly on the extent of the exchange reaction.